1. Field of the Invention
The present invention relates to a fine processing method including an etching process suitable for producing a semiconductor device.
2. Related Arts
To produce a semiconductor device, for example used as a semiconductor pressure sensor, conventionally, a silicon nitride (SiN) layer is formed on a silicon substrate, and etched by a photo-etching process into a predetermined shape to cause it to function as an etching mask. The silicon substrate on which the etching mask is formed is immersed in an etching solution (for example, a water solution of potassium hydroxide (KOH)), and etched through the etching mask. Accordingly, as shown in FIG. 9, a recess portion 22 of a predetermined shape is formed on the silicon substrate 21 so that a thin silicon diaphragm 24 is formed at the bottom of the recess portion 22.
In the etching process, because the SiN layer 25 functioning as the etching mask has sufficient strength and adhesive property to the silicon substrate 21, the etching mask is not easily cracked or separated from the silicon substrate 21. As shown in FIG. 9, however, inadequate erosion portions 23 are generated on the silicon substrate 21 exposed to the recess portion 22. Consequently, variation in the geometry of the recess portion 22 occurs, whereby dimensional accuracy of the diaphragm 24 is deteriorated.